This invention pertains to a composition for decontaminating biofilm-contaminated surfaces, particularly to a composition that both destroys the biofilm and kills bacteria.
Biofilms are microbial populations adherent to surfaces that are in constant or intermittent contact with water. Biofilms are typically composed of bacteria and other microorganisms in a biopolymer matrix, both produced by the microbial population and derived from the surrounding environment. A biofilm environment enhances microbial growth on surfaces in various ways. It allows a microbe to be retained on a surface instead of being swept away by a fluid, permits better nutrient assimilation, and provides the bacteria some degree of protection from phagocytes, antibiotics, immunoglobulins, surfactants and disinfectants. J. A. Mayo et al., xe2x80x9cBacterial Biofilm: A Source of Contamination in Dental Air-Water Syringes,xe2x80x9d Clinical Preventive Dentistry, vol. 12 (3), pp. 13-20 (1990).
Biofilms have deleterious effects on industrial and biological systems. Biofilms can cause corrosion, plugging of filters, fouling of heat exchangers, and reduction of flow through pipelines. Unwanted biofilms can accumulate in the distribution pipes of city water systems and in milk transfer pipes of the dairy industry. See, R. A. Heckmann, xe2x80x9cQuality control and evaluation of milking machines liners (inflations) and milk tubes using scanning electron microscopy and x-ray microanalysis,xe2x80x9d USA Microscopy and Analysis, November 1997, pp. 19-21(1997); and Mayo et al., 1990. Conditions such as dental plaque and diseases such as dental caries and endocarditis involve the accumulation of biofilms within the body.
Materials contaminated with biofilm bacteria are particularly difficult to sterilize or disinfect. The shape, size, and location of equipment often makes heat sterilization difficult or, in some cases, impossible. Moreover, many materials are not heat stable.
One area of particular concern is contamination of water lines in dental clinics. The dental unit water may be contaminated by the release of microorganisms from biofilms located on the lumen surfaces of the water lines. Dental unit water can harbor high concentrations of bacterial contaminants, with values ranging from 20,000 to 500,000 colony-forming units (cfu) of bacteria per milliliter (ml) of water. For comparison, faucet water from the same sites showed bacterial counts of 0 to 15 cfu/ml. Mayo et al., 1990. Organisms found in dental unit water include opportunistic pathogens that may cause harmful infections in immunocompromised patients. Additionally, the bleeding that commonly occurs during dental procedures exposes both healthy and immunocompromised patients to the possibility of infections.
Dental unit biofilms have been found to contain various species of Legionella bacteria, including the causative agent of Legionnaires"" disease, Legionella pneumophila. Biofilms in water lines may also harbor bacteria known to be involved in causing dental caries or periodontal diseases (Bacteroides, Fusobacterium, Lactobacillus, Peptostreptococcus, Streptococcus). C. H. Miller, xe2x80x9cMicrobes in Dental Unit Water,xe2x80x9d CDA Journal, vol. 24, pp. 47-52 (1996).
Mechanical and chemical methods aimed at reducing bacterial contamination of water lines have been unable to eliminate the problem of rapid reinfection of water lines. If a biofilm is not completely removed, bacteria remaining in the biofilm rapidly proliferate and reinfect the water lines. Flushing of high-speed handpieces and dental unit water lines as recommended by the Centers for Disease Control results in only a transient reduction in the microbial count of the effluent water. This procedure does not dislodge the biofilm on the lumen surface in the water lines, and therefore does not prevent recontamination of the water by bacteria remaining in the biofilm. C. H. Miller, CDA Journal, vol. 24, pp 47-52, 1996. In line filters can remove or reduce the bacteria found in dental unit water, but cannot directly reduce biofilms in the water lines. C. A. Murdoch-Kinch et al., xe2x80x9cComparison of Dental Water Quality Management Procedures,xe2x80x9d JADA, vol. 128, pp. 1235-1243 (1997). Other suggested treatments, including drying water lines or using steam to purge lines, are either not practical in dental water systems or not often used in practice because of the time and training necessary.
Methods using chemical disinfection to kill biofilm bacteria in dental unit water lines include using alcohol (70% v/v), povidone-iodine (10% solution), acids (e.g., a mixture of mandelic and lactic acids), sodium hypochlorite, and peroxyacids. See Abel et al., xe2x80x9cStudies on Dental Aerobiology, IV. Bacterial Contamination of Water Delivered by Dental Units,xe2x80x9d J. Dental Res., Vol. 50, pp. 1567-1569 (1971); and E. Peters et al., xe2x80x9cDental Unit Water Contamination,xe2x80x9d Journal of the Canadian Dental Association, vol. 62, pp. 492-495 (1996). Commercially available antiseptic compositions include chlorhexidine, BIOVAC(trademark) (chlorhexidine, EDTA, proteolytic enzymes, and a dispersing agent), EFFERDENT(trademark) (potassium monopersulphate, sodium borate, sodium lauryl persulfate, sodium bicarbonate, magnesium stearate, and simethicone), POLYDENT(trademark) (potassium monopersulphate, tetrasodium pyrophosphate, sodium bicarbonate, and sodium borate), STERISOLT(trademark) (chlorhexidine, glycerol, 38-F, and alcohol), THERASOL(trademark) (C-31G, sodium fluoride, glycerine, and alcohol), and PATHEX(trademark) (phenolic).
Another approach to killing biofilm bacteria is to damage bacterial proteins with denaturing agents such as glutaraldehyde or sodium lauryl sulfate (which has both denaturing and detergent properties). However, the biopolymer matrix surrounding biofilm bacteria reduces the effectiveness of many of these biocidal treatments by blocking access to the target organisms. As a result, many of these treatments cause only a temporary reduction in bacterial numbers until the remaining bacteria proliferate and reinfect both the surface and the liquids flowing over the biofilm-contaminated surface.
Peroxides have been used as a source of highly reactive free radicals to attack and disinfect biofilm-contaminated surfaces. Hydrogen peroxide is classified as xe2x80x9cgenerally recognized as safexe2x80x9d (GRAS) and is used in a 5% solution to wash fruits and vegetables. See G. M. Sapers et al. xe2x80x9cHydrogen peroxide disinfection of minimally processed fruits and vegetables,xe2x80x9d Food Technology, vol. 52, no. 2, pp 48-50, 1998). The anti-biofilm biocidal action of peroxides and persulfate is significantly enhanced by incorporation of transition metal catalysts into the surfaces to be cleaned. See P. Wood et al., xe2x80x9cSurface-catalysed disinfection of thick Pseudomonas aeruginosa biofilms,xe2x80x9d Journal of Applied Microbiology, vol. 84, pp. 1092-1098 (1998).
Although some treatments appear to effectively kill biofilm bacteria, they do not dislodge the biofilm matrix from surfaces. Alternately, treatments that attack the matrix do not necessarily kill the biofilm bacteria. Detergents (e.g., Tween 80) can be used to dislodge biofilm from small diameter dental unit waterlines, but detergent alone does not effectively destroy the microorganisms present in the biofilm.
U.S. Pat. No. 5,320,805 discloses a disinfectant comprising alkaline water-soluble salts having hydrogen peroxide crystallization (e.g., sodium carbonate-hydrogen peroxide of crystallization) and a positively charged phase transfer agent (e.g., phosphonium salt, sulfonium salt, or quaternary ammonium salt), which form a water- and lipid-soluble phase-transfer ion pair that can pass between aqueous and lipid phases.
U.S. Pat. No. 5,725,678 discloses cleaning organic residues from surfaces using hydrogen peroxide, where the effectiveness of the process is enhanced by iron or other catalysts or enhancers.
U.S. Pat. No. 5,344,652 discloses an anticorrosive microbiocidal solution that combines a mixture of acetic acid, hydrogen peroxide, peracetic acid, and water with a wetting agent.
U.S. Pat. Nos. 5,731,275 and 5,759,970 disclose a composition to clean and disinfect biofilm-contaminated surfaces containing all of the following: a detergent for reducing the surface tension of the biofilm, a denaturing agent for affecting the integrity of proteins and mucopolysaccharides of both the bacteria and the extracellular matrix, and a wide-spectrum disinfectant.
U.S. Pat. No. 5,489,434 discloses an antimicrobial composition comprising various combinations of a C5 peroxyacid, with a C1-C4 peroxyacid, or a C6-C18 peroxyacid.
The prior treatments suffer several disadvantages. Treatments using detergents, denaturants, and strong disinfectants often require extensive rinsing of the treated water lines or other surfaces before they are safe for human use again. Use of volatile compounds with strong odors (e.g., peracetic acid) can be disagreeable or even harmful; use of sodium hypochlorite (bleach; NaOCl) may cause corrosion of in-line metal valves; and use of steam or drying may cause long-term damage to the surfaces being decontaminated.
There remains a need for a safe composition that is effective for decontaminating water lines and other surfaces by killing bacteria and destroying at least a part of the biofilm.
We have discovered a novel composition for decontaminating biofilm-contaminated surfaces (the xe2x80x9cBiocidal Complexxe2x80x9d). The novel composition both kills bacteria and destroys at least a part of the biofilm. The composition comprises an effective amount of a free-radical-generating compound (e.g., hydrogen peroxide), a disinfectant from the xe2x80x9cGRASxe2x80x9d list of food-safe compounds (e.g., thymol), and an acid sulfate such as sodium bisulfate (NaHSO4) to acidify the solution and help catalyze free radical formation. A preferred method of using this invention employs a multi-component approach that permits long-term storage of the components in a stable, concentrated form. Immediately before use, the components are mixed and then applied to the biofilm-contaminated surface. A separate metal catalyst for the generation of free-radicals may be added to increase the production of free radicals in the Biocidal Complex. This invention offers a safe, effective, and easy method for disinfecting and decontaminating biofilm-contaminated surfaces, including water lines in dental units.